VSE: Imported audio not in-sync with video after 10 minutes
Bad sync between recording devices happens for many reasons, check out the wiki article 


  Digital or analog audio video streams or video files usually contain some sort of explicit AV-sync timing, either in the form of interleaved video and audio data or by explicit relative time-stamping of data. The processing of data must respect the relative data timing by e.g. stretching between or interpolation of received data. If the processing does not respect the AV-sync error, it will increase whenever data gets lost because of transmission errors or because of missing or mis-timed processing.


As the audio has drifted away from your pictures without a common reference I would suggest looking for easily identifiable sync points in both recordings. Split the audio at that point and drag it back to match the video. Depending on how fast the drift occurs will indicate how many splits you require. It could be one every few minutes if you're unlucky.

You can try to apply a minimal amount of pitch control on the audio strip. This will speed up the playback of the media by a certain amount, but its hard to be accurate as the wave form won't reflect the change, unless you render it out and re-import it. Use Blender's Audio Mixdown function to achieve this.